1. Field of the Invention
The present invention relates generally to ramps used to load and unload freight from shipping containers. In particular, the invention relates to a portable container ramp that can be transported by a forklift.
2. Description of the Prior Art
Container ramps are used to load and unload items to and from shipping containers like those carried by container ships. Shipping containers are often lifted from ships and placed on the dock or ground for loading and unloading. While on the ground, a difference in level exists between the floor of the shipping container and the surface on which it rests. Container ramps are used to bridge this difference in level. These ramps need to be portable for transport from one container to another. Forklift tractors are the vehicles of choice for transporting container ramps between shipping containers.
One of the challenges to transporting a container ramp is the difficulty in initially getting the forks of a forklift under the rear edge of a ramp, which normally rests in full contact with a supporting surface. Prior art attempts to solve this problem mostly involve a rear edge lifting mechanism having moving parts. The moving parts for these lifting mechanisms add substantially to the costs of the ramp and also require more maintenance than ramps not having moving parts.
Other ramps have attached chains that loop over the forks of a forklift for lifting and transporting. Lift chains have the disadvantage of requiring a helper to ready the chains and loop them over the forks of the forklift for lifting and transport. Worst yet, if a helper is not available, a forklift operator must dismount the forklift to ready the chains, thereby breaking up what should be a continuous operation.
One patent, U.S. Pat. No. 4,634,145 to Humped discloses a ramp that does not require a lifting mechanism or lift chains. Instead, the ramp disclosed by Humped has an internal lift engagement support plate structure that receives the forks of a forklift. One disadvantage of this design is the need for a forklift operator to use great precision to guide the forklift forks through openings in the ramp in order to reach the internal lift support plate structure. Another disadvantage is the complexity of manufacture involving the alignment of the internal support plate structure with the slot openings in the ramp. Therefore, a need remains for a container ramp of simple construction that can be easily transported by a forklift tractor.
The present invention is directed to a portable container ramp capable of supporting loads of considerable weight while bridging the difference in level between the floor of a shipping container and the surface on which the ramp rests. The invention relates especially to a container ramp that can be easily lifted and transported by an elevator type forklift tractor.
The present invention is a ramp having a front end that can be positioned up to the open end of a shipping container and a back end adapted to receive the forks of a forklift for lifting and transport. Generally, the ramp is made up of an upwardly inclined support structure having an upper surface that supports a load bearing plate and a lower surface that normally rests on the ground. The load bearing plate has an outer surface, an inner surface, a front edge, a back edge and side edges. The back edge includes at least one cutout section with a forward edge spaced above the support structure""s lower surface. The ramp further includes at least one lift plate that has a bottom surface that is substantially in a plane with the at least one cutout forward edge when the ramp is positioned horizontally, i.e., on the ground.
In a preferred embodiment, there are two spaced cutouts in the back edge of the load-bearing surface. Each of these two cutouts is sized to engage and guide a forklift fork. The spacing between the cutouts is set to receive the forks of a forklift adapted to a given separation distance. Preferably, the front edges of both cutouts are aligned and are parallel with the back edge of the load-bearing surface. Moreover, the forward edge of each cutout can be beveled on a downward slope to help guide the forklift""s forks to underneath the ramp. The bevel slope can range between 5 and 45 degrees. The preferred bevel slope is around 20 degrees.
Furthermore, in this preferred embodiment, sidewalls each having a railing section and a support section attach to the side edges of the load-bearing plate. A forward bracing plate near the ramp front end extends downwardly from the load-bearing plate inner surface and extends between and transverse to the sidewalls. Preferably, the upwardly inclined support structure is made up of a plurality of bracing plates extending downwardly from the load-bearing plate""s inner surface. The bracing plates and sidewall support sections have bottom edges forming the support structure""s lower surface.
Also, two lift plates extend downwardly between two pairs of the bracing plates. Both lift plates have a bottom surface that is substantially in a plane with the forward edges of the two cutouts when the ramp is positioned horizontally, i.e., resting on the ground. The spacing of the lift plates substantially equals that of the spacing of the two cutouts. Moreover, the cutouts and lift plates align defining a pathway that leads engaging forklift forks from the back end of the ramp to the front end of the ramp.
The preferred ramp also includes a forward section comprising a lip for extending over the floor of a shipping container. The lip comprises a horizontal lower surface with a forward edge that extends from the front end of the ramp. An upper surface for the lip is made from a section of the load-bearing surface that extends beyond the front end of the ramp and inclines slightly downward such that the load-bearing surface front edge joins with the horizontal surface""s forward edge. Preferably, the lip upper surface inclines downwardly at an angle of around 10 degrees. It is also preferred that the load-bearing surface has a texture to prevent slipping while loading or unloading a shipping container. The texture can be any texture that makes for a non-slip surface. An example would be a texture like that found on the surface of a type of steel plate commonly known as diamond plate.
To lift the ramp, a forklift operator drives the fork tips of a forklift tractor under both cutout forward edges. As the forklift tractor is driven forward, the edges of the cutouts guide the forklift""s forks underneath the lift plates. Normally, the forklift operator continues driving the forklift forward until the tips of the forks extend slightly beyond ramp front end. At this point the forklift""s forks can be raised to lift the ramp. When lifted, the weight of the ramp is distributed across the forklift""s fork at the cutout forward edges, lift plates, and forward bracing plate.
Once lifted, the ramp can be carried on the forklift""s forks to a shipping container to be loaded or unloaded. Since the front end of the ramp is facing away from the forklift tractor when carried, the ramp front end can be maneuvered just up to the open end of a shipping container. When the ramp is lowered, the support surface will come to rest on the ground and the ramp lip will extend into the shipping container. Ideally, the lip lower surface will come to rest on the floor of the container. However, slight differences in level may allow a small gap to exist between the lip""s lower surface and the container floor. Once the ramp is resting horizontally on the ground, the forklift tractor is backed away and the forklift forks withdraw from beneath the cutout leading edges.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment.